The present invention relates to high-pressure reciprocating pumps for producing high pressure or superhigh pressure in a liquid phase and, more particularly, pertains to high-pressure reciprocating pumps suited for pressurizing a slurry and transferring it under pressure.
A conventional high-pressure reciprocating pump is constructed such that a plunger is made to move back and forth inside a cylinder, a channel connected to an inlet pipe or a discharge pipe is opened and closed by a valve in synchronism with movements of the plunger to vary the volume of a fluid within a pumping chamber, and the fluid is thereby transferred to a high-pressure side.
This type of high-pressure reciprocating pumps is used for cleaning wastewater gutters in chemical plants, food processing plants and buildings, for cleaning ships, and for maintaining and cleaning civil engineering and construction machines. Also, these pumps are incorporated in such equipment as water-jet cutting machines or electronic parts cleaning systems.
FIGS. 8A and 8B illustrate a general construction of a high-pressure reciprocating pump mainly comprising a crankshaft 61 provided inside a crankshaft case 60, a connecting rod 62 whose one end is connected to the crankshaft 61, a plunger 64 which is connected to the other end of the connecting rod 62 and moves back and forth inside a cylinder 63, and a valve case 65 which is affixed to a foremost end of the crankshaft case 60, closing its opening.
The plunger 64 moves to the left in each intake stroke of the pump as shown in FIG. 8A. As the inner volume of the valve case 65 increases corresponding to the amount of leftward movement of the plunger 64, the internal pressure of the valve case 65 is reduced. Forced by atmospheric pressure, a fluid is drawn in through an intake port 66 and introduced into the valve case 65 through an inlet valve 67. In each output stroke, the plunger 64 moves to the right as shown in FIG. 8B and the fluid in a forward part of the plunger 64 pushes an outlet valve 68 to its open position and is discharged through a delivery port 69.
Pressure in a fluid outflow and flow rate vary in the aforementioned construction in which the plunger 64 is made to move back and forth. Generally, this type of construction employs an accumulator to absorb and reduce pressure pulsation which occurs in outflow tubing, or an increased number of cylinders, forming a multi-cylinder structure, in order to increase the number of output strokes per rotation of the crankshaft and thereby produce a more uniform flow.
In the above construction, the plunger 64 is joined to a piston 64a to form a single structure by tightening their externally and internally threaded portions together.
The valve case 65 of such conventional high-pressure reciprocating pump is usually a blocklike heavy object which is one-piece formed by metal casting or forging, with a pressurizing chamber 65a, an intake channel 65b and a discharge channel 65c formed in the valve case 65 in a complex configuration by carrying out precision cutting operation using a machine tool. This makes it difficult to create each pressurizing chamber and valve section. Especially when assembling a multi-cylinder type reciprocating pump or disassembling it for servicing, no matter whether it is relatively small, more than one worker and a crane are required to handle the pump and great care must be taken not to break or otherwise damage any plungers or packing, because its valve case is a heavy object incorporating multiple pressurizing chambers and valve sections. Thus, one problem of the conventional construction is poor labor efficiency. Another problem is that the whole valve case must be removed from the crankshaft case.
Furthermore, in the conventional valve case 65 in which the pressurizing chamber 65a, the intake channel 65b and the discharge channel 65c are formed by cutting operation, the intake channel 65b or the discharge channel 65c is made perpendicular to the pressurizing chamber 65a and, therefore, edges are formed where the pressurizing chamber 65a and the intake channel 65b or the discharge channel 65c adjoin. If such edges are exposed to high-pressure or superhigh-pressure pulsating fluid flows when the high-pressure reciprocating pump is in operation, low-cycle fatigue fracture is likely to occur from the edges, eventually causing a breakdown of the valve case 65.
It might be possible to employ a more expensive high-strength material or a rigid material which has been treated by a quench hardening process, for example, to avoid such breakdown. This would, however, make it infeasible to reduce the weight of the valve case 65 and its machining and handling would become more difficult.
The driving piston 64a and the plunger 64 are joined together to form a single structure as stated above. For this reason, extremely high accuracy is required to provide good sealing for the plunger 64 when the pressurizing chamber 65a is formed by assembling the crankshaft case 60 and the valve case 65.
To achieve such high accuracy in assembling the heavy high-pressure reciprocating pump, however, an extremely high level of skill has been required. Although this does not cause any serious problem if the plunger 64 is made of metal, there arises a problem that the plunger 64 could easily break if it is of a type coated with such fragile material as ceramics and is not properly centered with respect to the piston 64a due to poor positioning accuracy. Furthermore, low-accuracy centering of the plunger 64 could cause eccentric wear of its sealing device, resulting in a shortened useful life of sealing and deterioration of the reliability of the high-pressure reciprocating pump.
Another problem potentially encountered with this type of high-pressure reciprocating pump is that leakage could occur at sealing of sliding parts of the pump when transferring a pressurized slurry, especially a slurry containing an inorganic substance.